[sdiy] MN3007 Chorus Acting Weird

[Jacob Watters]

That makes sense. I didn't even consider phasing.

Thanks again!

*Jacob Watters*
JacobWatters.com <http://jacobwatters.com/>


On Sat, Feb 15, 2025 at 5:44 PM Richie Burnett <rburnett at richieburnett.co.uk>
wrote:

> A sinewave mixed with a time-delayed (phase-shifted) sinewave just results
> in another sinewave with different amplitude and phase.  So you mostly
> just
> perceive a variation in the intensity (volume) as you get
> constructive/destructive interference between the dry and delayed signal
> at
> that one frequency.
>
> If you fire a saw or square into the Chorus effect there's a rich spectrum
> of harmonics and you hear that lush "swooshing" chorus effect as you get
> constructive & destructive interference at all of the harmonic frequencies
> at different times during the periodic sweeping delay.  The movement in
> the
> resulting spectrum is much more complex and interesting to the ear.
>
> The delay time in cheap BBD chorus effects is also typically only 5ms or
> thereabouts, so you need a reasonably high pitch input signal before you
> get
> much "beating" at the actual fundamental frequency of the note.
>
> -Richie,
>
>
>
> -----Original Message-----
> From: Jacob Watters
> Sent: Saturday, February 15, 2025 10:16 PM
> To: Richie Burnett
> Cc: SDIY
> Subject: Re: [sdiy] MN3007 Chorus Acting Weird
>
>
> You were correct! I used a square wave, and I could immediately hear a
> normal chorus effect. I checked the scope, and I could see left and right
> movement.
>
> I am curious to learn more - is this because the BBD circuit works on a
> limited frequency range, and a low frequency sine is outside of that
> range,
> but the harmonics in a square wave are within the range? This would
> explain
> some of the unique character that people say a BBD has.
>
> Thank you so much!
>
> I am going to swap the rate trimpot for a panel mounted pot, and then this
> thing is ready to use :)
>
> Best regards,
>
> Jacob Watters
> JacobWatters.com
>
>
>
>
> On Sat, Feb 15, 2025 at 4:50 PM Richie Burnett
> <rburnett at richieburnett.co.uk> wrote:
> Try testing it with a sawtooth or square waveform.  With just a sinewave
> you
> can only really get amplitude modulation, especially if the test tone is
> quite a low pitch.  And that could sound like panning if you alternately
> get
> constructive interference on one side and destructive on the other side of
> the stereo image.  With a bright saw or squarewave at a decent pitch you
> should be able to hear some periodic detuning or at least some "phasing"
> between the dry and the chorused waveform edges.
>
> -Richie,
>
>
>
> -----Original Message-----
> From: Jacob Watters via Synth-diy
> Sent: Saturday, February 15, 2025 9:35 PM
> To: Richie Burnett
> Cc: SDIY
> Subject: Re: [sdiy] MN3007 Chorus Acting Weird
>
>
> I am testing it with a sine wave from a signal generator. When I look at a
> scope, I only see vertical movement. When I listen with my ears, I only
> hear
> panning.
>
> I found this photo of the service manual. It's difficult to read the exact
> values, but maybe someone familiar with the IC will be able to tell how it
> should be functioning. The BBD part is in the rectangle at the bottom with
> the "DC 1/2" label.
>
>
> https://rvb-img.reverb.com/image/upload/s--wzg-Dhdj--/f_auto,t_supersize/v1669410662/zuo0v17w68dkc6c0n99s.jpg
>
> Jacob Watters
> JacobWatters.com
>
>
>
> On Sat, Feb 15, 2025 at 4:28 PM Richie Burnett
> <rburnett at richieburnett.co.uk> wrote:
> What input signal are you testing it with?
>
> -Richie,
>
>
> -----Original Message-----
> From: Jacob Watters via Synth-diy
> Sent: Saturday, February 15, 2025 9:17 PM
> To: SDIY
> Subject: [sdiy] MN3007 Chorus Acting Weird
>
>
> I am repairing a Yamaha KM602 mixer, which has a builtin MN3007 circuit.
> The
> chorus circuit behaves a bit odd. Instead of being a modulated delay that
> causes a pitch shift, it seems to behave like an auto-pan circuit. The
> sound
> level increases on one side, while decreasing on the other, and alternates
> back and forth. It is labelled as CHORUS on the front panel, so that is not
> the behavior that I expected.
>
> Is this normal, or is something wrong with the circuit?
>
> I tried finding a pdf of the service manual online, but I was unsuccessful.
> Does anyone have the service manual and can provide some input as to how
> the
> circuit should work?
>
>
> Thanks for your help!
>
> Best regards,
>
> Jacob Watters
> JacobWatters.com
>
>
>
>
>
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